Methods for improved growth of group III nitride buffer layers

ABSTRACT

Methods are disclosed for growing high crystal quality group III-nitride epitaxial layers with advanced multiple buffer layer techniques. In an embodiment, a method includes forming group III-nitride buffer layers that contain aluminum on suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. A hydrogen halide or halogen gas is flowing into the growth zone during deposition of buffer layers to suppress homogeneous particle formation. Some combinations of low temperature buffers that contain aluminum (e.g., AlN, AlGaN) and high temperature buffers that contain aluminum (e.g., AlN, AlGaN) may be used to improve crystal quality and morphology of subsequently grown group III-nitride epitaxial layers. The buffer may be deposited on the substrate, or on the surface of another buffer. The additional buffer layers may be added as interlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).

RELATED APPLICATIONS

This application claims the benefit of Provisional Application No.61/488,675, filed May 20, 2011, which is incorporated herein byreference.

The United States Government has rights in this invention pursuant toContract No. DE-EE0003331 between the United States Department of Energyand Applied Materials, Inc.

FIELD

Embodiments of this invention relate to methods for improved growth ofgroup III-nitride buffer layers of semiconductors in processing systems.

DESCRIPTION OF RELATED ART

Aluminum (Al) containing III-V compound semiconductors are ofsignificant value since they are used in the fabrication of manyelectronic devices. The group III-Nitrides GaN, AlN and AlGaN alloys areextremely important materials with widespread applications foroptoelectronics (e.g. solid state lighting) and high power electronics.Metal-organic vapor phase epitaxy (MOVPE) is the primary depositionmethodology, but hydride vapor phase epitaxy (HVPE) is an alternativeepitaxial growth method of group III-nitrides. In general, the HVPEprocess involves the reaction of one or more metallic halides with ahydride. For the growth of III-nitride materials, typically metallicchlorides and ammonia (NH3) are used.

One challenge with the use of aluminum trihalides in AlN HVPE process isthe homogeneous reactions and as a result AlN particles formation in thegas phase. It has been shown that, together with formation of AlN films,some particles are formed in the gas phase. The one-operation overallhomogeneous reaction for AlN particles formation is the same as forheterogeneous reaction, but the intermediate reaction paths will bedifferent. The identities of reaction intermediates involved in thehomogeneous reactions are usually difficult to be determinedexperimentally. Generally, if aluminum trihalide and NH3 meet eachother, adduct compounds AlRx-NHx type (where x=1-3, and R=Cl, Br, or I)may appear as a result of gas-phase reactions. The simultaneousformation of oligomeric forms is also preferable. The large amounts ofthe monomers and high-order oligomers in the gas phase finally producesmall suspended particles of AlN in the reactor chamber.

When aluminum trichloride (AlCl3) mixes with NH3, they reactinstantaneously producing AlN nanoparticles in the gas phase. Theone-operation overall homogeneous reaction for AlN particles formationfollows below.AlCl3(g)+NH3(g)=AlN(particles)+3HCl(g)  (1)

Premature premixing gases at low temperature, large volume of thedeposition chamber, and low total gas flow can significantly increasenominal residence time of AlN nanoparticles in the reactor. As a result,the size of AlN particles will be increased. The high residence time andhigh partial pressure of AlCl3 can lead to visible AlN powder in the gasphase.

AlN particles were directly observed in the AlCl3-NH3-Ar system in theatmospheric hot wall HVPE reactor without any additional optical tools(like in situ laser light scattering) by a prior approach. During thegrowth process aerosol in reactor is present. It looks like narrowmist-strip located at 2-3 mm away from the reactor walls.

The homogeneous formation of AlN powder in the HVPE process may beexplained on the basis of a model suggested by another prior approach.The gas-phase reactions are as following:AlR3(g)+NH3(g)=AlR3−NH3(s)  (2)AlR3−NH3(s)=AlR2−NH2(s)+HR(g)  (3)AlR2−NH2(s)=AlR−NH(s)+HR(g)  (4)AlR−NH(s)=AlN(s)+HR(g)  (5),where R=Cl, Br, or I.

So, AlN nanoparticles (AlN powder) represent the end product of a chainof gas-phase chemical reactions.

Using AlCl3 and NH3, as the parent species, another approach depositedaluminum nitride in a reactor consisted of a premixing zone (460 degreesC.), a rising-temperature zone (from 460 degrees C. to the reactiontemperature), a reaction zone (constant at a temperature ranging from700 to 1100 degrees C.), and a particle collection zone (600 degreesC.). This approach suggests that the chemical vapor deposition processstarts with formation of the adduct molecules AlCl3-(NH3)x, when AlCl3and NH3 are mixed in the premixing zone of a reactor. These adductmolecules form clusters and AlN particles in the gas phase. Theproduction rates of AlN layers on substrates and AlN particles in thegas phase were independently determined in AlCl3-NH3-He system.Formation of AlN clusters, ranging in size from 0.8 nm (700 degrees C.)to 0.5 nm (1100 degrees C.) was found to be a key process in the rapidgrowth of AlN.

However, the homogeneous process and AlN particles that form in the gasphase can lead to negative effects on heterogeneous AlN layerdeposition. The negative effects include a drop in deposition rate andyield and poor thickness uniformity.

The formation of particles in the gas phase is the possible cause formacro contaminants and other structural defects in the films. Thesurface roughness can also be dependent on parasitic homogeneousreactions.

Thus, the participation of AlN particles in the surface reaction(dropping on the surface of AlN epitaxial layer) depends heavily on thechamber design and process conditions, i.e. temperature, speciesconcentrations, gas velocity and total pressure. Homogeneous gas phasereactions in AlCl3-NH3 HVPE systems hinder the growth of good qualityepitaxial AlN films.

SUMMARY

Methods are disclosed for growing high crystal quality group III-nitrideepitaxial layers with advanced multiple buffer layer technique. In anembodiment, a method includes providing a suitable substrate in aprocessing chamber of a hydride vapor phase epitaxy processing system.The method includes forming group III-nitride buffer layers that containaluminum by flowing an ammonia gas into a growth zone of the processingchamber, flowing an one or more metal halide containing precursors(wherein at least one is aluminum halide containing precursor) to thegrowth zone and at the same time flowing additional hydrogen halide orhalogen gas into the growth zone of the processing chamber. Theadditional hydrogen halide or halogen gas that is flowed into the growthzone suppresses homogeneous particle formation during deposition ofbuffer layers. Some combinations of low temperature buffers that containaluminum (e.g., AlN, AlGaN) and high temperature buffers that containaluminum (e.g., AlN, AlGaN) may be used to improve crystal quality andmorphology of subsequently grown group III-nitride epitaxial layers.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure is illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings, in which:

FIG. 1 is a flowchart that illustrates a method for enhancing growth ofa high-quality group III-nitride film (e.g., GaN thin film) with a lowtemperature buffer layer in accordance with one embodiment;

FIG. 2 is a flowchart that illustrates a method for enhancing growth ofa high-quality group III-nitride film (e.g., GaN thin film) with a hightemperature buffer layer in accordance with one embodiment;

FIG. 3 a illustrates an AFM image 300 of a 1 micron by 1 micron sapphiresubstrate surface;

FIGS. 3 b-3 f illustrate the effect of additional Cl2 flow on a surfacemorphology of a high temperature AlN buffer layer deposited on thesapphire substrate in accordance with one embodiment;

FIG. 4 illustrates the root-mean-square roughness (Rms) in nanometers ofhigh temperature AlN buffers that are deposited on a sapphire substrateat different flows of additional Cl2 during the AlN deposition operationin accordance with one embodiment;

FIGS. 5 a-5 f illustrate several examples of locations of multiplebuffers for GaN deposition on a sapphire structure with a HVPE system inaccordance with one embodiment;

FIG. 6 illustrates a method for enhancing growth of a high-quality groupIII-nitride (e.g., GaN, AlGaN) layers with multiple buffer layers grownin a HVPE system in accordance with one embodiment;

FIG. 7 a illustrates an X-ray rocking curve for on-axis (002) peak andFIG. 7 b illustrates an X-ray rocking curve for an off-axis (102) peakfor 4.8 μm GaN deposited on a (0001) sapphire substrate in accordancewith one embodiment;

FIG. 8 illustrates an HVPE apparatus in accordance with one embodiment;

FIG. 9 illustrates a physical structure of a cluster tool schematicallyin one embodiment; and

FIG. 10 illustrates a cross-sectional view of a device in accordancewith one embodiment.

DETAILED DESCRIPTION

In the following description, numerous details are set forth. It will beapparent, however, to one skilled in the art, that the presentdisclosure may be practiced without these specific details. In someinstances, well-known methods and devices are shown in block diagramform, rather than in detail, to avoid obscuring the present disclosure.Reference throughout this specification to “an embodiment” means that aparticular feature, structure, function, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrase “in an embodiment” invarious places throughout this specification are not necessarilyreferring to the same embodiment of the invention. Furthermore, theparticular features, structures, functions, or characteristics may becombined in any suitable manner in one or more embodiments. For example,a first embodiment may be combined with a second embodiment anywhere thetwo embodiments are not mutually exclusive.

In one embodiment, an improved method for growing III-nitridesemiconductor epitaxial layers containing aluminum by hydride vaporphase epitaxy (HVPE) is disclosed. In one embodiment, the forming an AlNlayer (or Al-containing group III-nitride layer) is conducted by flowingammonia gas and aluminum halide containing precursor (or at least onealuminum halide containing precursor) into a growth zone of theprocessing chamber, and at the same time flowing hydrogen halide orhalogen gas into the growth zone of the processing chamber. The hydrogenhalide or halogen gas that is flowed into the growth zone suppresseshomogeneous formation of AlN (or Al-containing group III-nitride)particles. For example, AlN layer may be fabricated on suitablesubstrate with high quantities of aluminum trichloride (AlCl3) gas andammonia gas. The method utilizes additional Cl2 gas to suppresshomogeneous formation of AlN particles during hydride vapor phaseepitaxy of AlN layers. The suppression of homogeneous formation of AlNby introduction of Cl2 gas in the processing chamber during depositionoperation essentially improves crystal quality and morphology of theepitaxial layers grown on suitable substrates. As a result ofsuppression of homogeneous formations, deposition rate of AlN becomeshigher, product yield increases, and thickness uniformity improves. Inan alternative embodiment, another halogen gases (e.g., bromine (Br2)gas, iodine (I2) gas) may be used for suppression of homogeneousparticle formation during deposition of AlN layers (or Al-containinggroup III-nitride layer).

In one embodiment, the method also enables the growth of Al-containingIII-nitride compound semiconductors buffer layers (initial layers,nucleation sites) on suitable substrates for subsequent high quality GaN(or group III-nitride semiconductor) deposition.

A previous approach to grow AlN and AlGaN layers by HVPE withsuppression of AlN (or AlGaN) homogeneous formation used HCl as anactive gas. Conventional AlN HVPE process (involving aluminumtrichloride and ammonia as active gases) starts with formation of theadduct molecules, which form clusters and AlN particles in the gasphase. Introduction of HCl gas in the chamber during depositionoperation suppresses homogeneous formation of adduct molecules, clustersand AlN particles. The suppression mechanism includes inhibition anddissolution of homogeneous species after absorption of HCl molecules onthe surface of the species.

The use of Cl2 for suppression of AlN (or AlGaN) homogeneous formationhas a significant advantage over traditional suppression with HCl due tohigher efficiency. The bond energies for HCl and Cl2 are 431 kJ/mol and243 kJ/mol, correspondingly. The Cl—Cl bond is weakly bound compared tothe H-CI bond. So, a more rapid decomposition of the Cl2 with respect tothat of HCl would contribute to the increase in the dissolution rate.The suppression mechanism includes inhibition and dissolution ofhomogeneous species after absorption of Cl2 molecules on the surface ofthe species.

This additional Cl2 gas may act also as etchant for epitaxial AlN (orIII-nitride semiconductor compounds containing aluminum). To eliminatepossible negative effect of etching, an optimal partial concentration ofCl2 and temperature of the deposition have to be defined for eachreactor design.

The present disclosure may be used during aluminum containingIII-nitride buffers (initial layers) deposition on suitable substratesfor subsequent high quality epitaxial GaN (or III-nitride semiconductor)growth. The present disclosure discloses a method of growing AlN (orAl-containing III-nitride) buffers using additional hydrogen halide orhalogen gas for suppression of homogeneous particle formation duringbuffer deposition operation. The crystalline quality of the GaN layersgrown on AlN buffers deposited by this method is comparable to (if notsuperior to) the highest-quality GaN layers grown by MOCVD or HVPEreported in the literature.

In one embodiment, the average deposition time for the buffer depositionoperation is not so long (e.g., approximately several minutes), so theefficiency of homogeneous suppression becomes less critical. In thiscase, additional HCl gas as an alternative to Cl2 gas may be used. Thepresent disclosure discloses a method of growing AlN buffer layers(initial layers, nucleation layers) using additional HCl gas forsuppression of homogeneous particle formation during buffer depositionoperation. These buffers may be used for subsequent high quality GaN (orIII-nitride semiconductor) growth. In an alternative embodiment, anotherhydrogen halide gases (e.g., hydrogen bromide (HBr) gas, hydrogen iodide(HI) gas) may be used for suppression of homogeneous particle formationduring buffer deposition operation

In one embodiment, the forming an AlN buffer layer is conducted byflowing ammonia gas and an aluminum halide containing precursor into agrowth zone of the processing chamber, and at the same time flowinghydrogen halide or halogen gas into the growth zone of the processingchamber, wherein the hydrogen halide or halogen gas that is flowed intothe growth zone suppresses homogeneous formation of AlN particles. Thestopping of an aluminum containing precursor flow coming to theprocessing chamber (or growth zone of the processing chamber) at thesame time as stopping hydrogen halide or halogen gas (at the end offorming the AlN buffer layer) is critical for present disclosureperformance. The flowing of aluminum halide containing precursor withoutthe hydrogen halide or halogen gas will immediately lead to particlesformation. However, the stopping of an aluminum containing precursorflow at the same time as stopping hydrogen halide or halogen gas islimited by the difficulty which originate from aluminum halide gasformation (usually metallic Al reacts with HCl or Cl2 in separate zoneupstream of the reactor). In one embodiment, the flow of the aluminumhalide containing precursor is stopped while the halogen gas and ammoniaare continuing to flow into the growth zone of the processing chamberfor a time period. After the flow of metal halide containing precursoris turned off, the additional hydrogen halide or halogen gas flow intothe growth zone continues for a certain time period (e.g., 0-5 minutes)to eliminate possible particle creation. The certain time period (delaytime) has to be experimentally defined for each chamber design.

FIG. 1 is a flowchart that illustrates a method for enhancing growth ofa high-quality group III-nitride epitaxial layer (e.g., GaN layer) witha low temperature (e.g., temperature less than 900 degrees C., 500-800degrees C., 600-700 degrees C.) buffer layer containing aluminum inaccordance with one embodiment. The method includes growing an in situlow temperature buffer layer (or initial layer, or nucleation layer)containing aluminum (e.g., AlN, AlGaN) on suitable substrate (e.g.,sapphire, SiC, Si, AlN). The buffer layer containing aluminum is grownwith suppression of homogenous particle formation. Then, a subsequenthigh temperature group III-nitride (e.g., GaN) deposition occurs in theHVPE processing systems.

In one embodiment, a substrate is provided (e.g., aluminum oxidecontaining substrate, sapphire substrate, (0001) sapphire substrate) forthe growth of group III-nitride layers (e.g., GaN, AlN, AlGaN) at block102. The substrate is loaded into a HVPE processing system at block 104.Then, initial process conditions are established in the processingsystem at block 106. These process conditions may include setting thepressure (e.g., 50-800 Torr, 400-500 Torr), setting the nitrogencontaining material (e.g, nitrogen gas, nitrous oxide, ammonia,hydrazine, diimide, hydrazoic acid, etc) to a flow rate (e.g., 2-10standard liters per minute (SLM), 2-4 SLM), and then ramping a substratecarrier temperature to a first temperature (e.g., temperature greaterthan 900 degrees C., 950-1050 degrees C.). Once the temperature reachesthe set point, the substrate is under nitridization for a certain timeperiod (e.g., 5-15 minutes) at block 108. After nitridization, thesubstrate carrier is cooled down to a second temperature (e.g.,temperature less than 900 degrees C., 500-800 degrees, 600-700 degreesC.) at block 110. When the temperature set point is reached, a lowtemperature group III-nitride buffer layer containing aluminum (e.g.,AlN, AlGaN) deposition starts at block 114. The buffer layer is grownwhile suppressing homogenous particle formation (e.g., AlN, AlGaN) basedon flowing a halogen gas (e.g., additional chlorine gas) to the growthzone. Alternatively, a hydrogen halide (e.g., hydrogen chloride (HCl))gas flows into the growth zone to suppress homogeneous particleformation. The process conditions for the buffer layer deposition mayinclude flowing one or more metal halide precursors (e.g., at least onealuminum halide containing precursor (e.g., AlCl3, AlCl, AlBr, AlBr3,AlI, AlI3, GaCl, GaCl3, etc.)) with a carrier gas into the growth zoneof the HVPE system at block 114. An aluminum chloride precursor may beformed by flowing chlorine gas (Cl2) to a metal source (e.g., analuminum source) located in separate zone (upstream of the depositionzone) at a flow rate and time period (e.g., 10-150 sccm for 30 secondsto 5 minutes). Alternatively, the hydrogen halide (e.g., HCl) gas isflowed over an Al source to form the aluminum chloride precursor at aflow rate and time period (e.g., 20-300 sccm for 30 seconds to 5minutes). The Al source may be solid and have a temperature from 200degrees C. to the Al melting point temperature (e.g., about 660 degreesC.). The Al source may be liquid and have a temperature greater than theAl melting point temperature. In another embodiment, a source of liquidGa is also used to form a gallium chloride precursor (e.g., GaCl, GaCl3)in separate zone upstream of the deposition zone.

At the same or approximately the same time (e.g., 0-1 min before) of theintroduction of the metal halide precursors into the growth zone, ahalogen gas (e.g., chlorine (Cl2) gas) or a hydrogen halide gas (e.g.,hydrogen chloride (HCl) gas) flow is introduced to the growth zone(e.g., 200-1100 sccm, 400-900 sccm) at block 116. After the flow of themetal halide precursors is turned off, the halogen gas or the hydrogenhalide gas flow can keep flowing for a time period (e.g., 0-5 minutes)at block 118. The buffer layer is deposited based on the reaction of theammonia, one or more metal halide precursors, and a halogen gas or ahydrogen halide gas in the growth zone. For example, an AlN buffer layeris deposited based on the reaction of ammonia, aluminum halidecontaining precursor (e.g., AlCl3, AlCl, AlBr3, AlBr) and chlorine gas(or hydrogen chloride gas) in the growth zone. Alternatively, an AlGaNbuffer layer is deposited based on the reaction of ammonia, aluminumhalide containing precursor (e.g., AlCl3, AlCl, AlBr3, AlBr), galliumhalide containing precursor (e.g. GaCl, GaCl3), and additional chlorinegas (or hydrogen chloride gas) in the growth zone. The additionalchlorine gas (or hydrogen chloride gas) in the growth zone suppresseshomogeneous particle formation during the buffer deposition operation.

After the halogen gas or a hydrogen halide gas flow is turned off, thesubstrate carrier temperature starts to ramp to a third temperature(e.g., temperature greater than 900 degrees C., 980-1080 degrees C.) atblock 120. During this operation, ammonia flow switches to 1-22 SLM.Once the substrate carrier temperature reaches the third temperature,chlorine (Cl2) gas flow over a metal source (e.g., Ga source) isintroduced to a flow rate (e.g., 50-400 sccm) for group III-nitridegrowth (e.g., GaN growth) at block 122. After a 3-30 minute deposition,when the desired GaN thickness is achieved, the chlorine gas flow overthe metal source is interrupted and the substrate carrier is cooled downwhile flowing ammonia gas to preserve the group III-nitride layer atblock 124. In an alternative embodiment, the chlorine (Cl2) gas flow ofoperations 122 is replaced with hydrogen chloride (HCl) gas flow.

In one embodiment, GaN layers were deposited on in situ low temperatureAlN buffers in a vertical 28×2 inch capacity Ga—Al—Cl2-NH3-N2 HVPEsystem. In the separate Al and Ga source zones, the Cl2 reacted with themetals (Al and Ga) to form AlCl3 and GaCl, respectively. The chlorideswere transported by N2 and mixed with ammonia in the growth zone. 1.5 μmand 3 μm thick GaN films have been grown on (0001) sapphire substratesusing process conditions described above with a growth rate between 10and 15 μm/hr. The roughness of the GaN layers is in the range of 2-3 nm.The layer quality has been investigated by X-ray diffraction. The FWHMof reflections (002) and (102) is used to determine the tilt and twiststructure of the GaN layer. The FWHM of the co-scan rocking curves for(002) and (102) reflections for 1.5 μm thick GaN layers were in therange of 70-250 arcsec and 350-600 arcsec, respectively. The FWHM of theco-scan rocking curves for (002) and (102) reflections for 2.5 μm thickGaN layers were in the range of 130-300 arcsec and 300-500 arcsec,respectively.

FIG. 2 is a flowchart that illustrates a method for enhancing growth ofa high-quality group III-nitride epitaxial layer (e.g., GaN layer) witha high temperature (e.g., 900 degrees C. or higher) buffer layercontaining aluminum in accordance with one embodiment. The methodincludes growing an in situ high temperature buffer layer (or initiallayer, or nucleation layer) containing aluminum (e.g., AlN buffer layer)on suitable substrate (e.g., sapphire, SiC, Si, AlN). The buffer layercontaining aluminum is grown with suppression of homogenous particleformation. Then, a subsequent high temperature group III-nitride (e.g.,GaN) deposition occurs in the HVPE processing systems.

In one embodiment, a high temperature buffer layer or initial layer ornucleation layer (e.g., AlN buffer, AlGaN buffer) is deposited toenhance a subsequent high quality group III-nitride epitaxial layer(e.g., GaN) deposition. A substrate (e.g., aluminum oxide containingsubstrate, sapphire substrate, (0001) sapphire substrate) is providedfor the growth of the group III-nitride layer at block 202. Thesubstrate is loaded into a HVPE reactor at block 204. Then, initialprocess conditions are established in the processing system at block206. These process conditions may include setting the pressure (e.g.,50-800 Torr, 400-500 Torr), setting the nitrogen containing material(e.g, nitrogen gas, nitrous oxide, ammonia, hydrazine, diimide,hydrazoic acid, etc) flow to 1-15 SLM, and the ramping a substratecarrier to a first temperature (e.g., temperature greater than or equalto 900 degrees C., 950-1050 degrees C.). Once the temperature reachesthe set point, the substrate is under nitridization for a certain timeperiod (e.g., 2-15 minutes) with the ammonia flow being set to a flowrate (e.g., 2-12 SLM) at block 208.

After nitridization, the substrate carrier temperature is ramped (up ordown) to a second temperature (e.g., temperature greater than or equalto 900 degrees C., 930-1050 degrees C.) at block 210. In one embodiment,the first temperature is equal to the second temperature. When thetemperature set point is reached, a high temperature group III-nitridebuffer layer containing aluminum (e.g., AlN, AlGaN) deposition starts atblock 212. The buffer layer is grown while suppressing homogenousparticle formation based on flowing additional chlorine (Cl2) to thegrowth zone. Alternatively, hydrogen chloride (HCl) gas flows into thegrowth zone to suppress homogeneous particle formation. The processconditions for the buffer layer deposition may include flowing one ormore metal halide precursors (e.g., at least one aluminum halidecontaining precursor (e.g., AlCl3, AlCl, AlBr, AlBr3, AlI, AlI3, GaCl,GaCl3, etc.)) with a carrier gas into the growth zone of the HVPE systemat block 212. An aluminum chloride precursor may be formed by flowingchlorine gas (Cl2) to an aluminum source located in separate zoneupstream of the growth zone (Al source zone of the reactor) at a flowrate and time period (e.g., 10-150 sccm for 30 seconds to 5 minutes).Alternatively, HCl gas is flowed over an Al source to form the aluminumchloride precursor at a flow rate and time period (e.g., 20-300 sccm for30 seconds to 5 minutes). The Al source may be solid and have atemperature from 200 degrees C. to the Al melting point temperature(e.g., about 660 degrees C.). The Al source may be liquid and have atemperature greater than the Al melting point temperature. In anotherembodiment, a source of liquid Ga located in separate zone upstream ofthe reactor (Ga source zone of the reactor) is used to form a galliumchloride precursor (e.g., GaCl, GaCl3).

At the same or approximately the same time (e.g., 0-1 min before) of theintroduction of the metal halide precursors into the growth zone, ahalogen gas (e.g., chlorine (Cl2) gas) or a hydrogen halide gas (e.g.,hydrogen chloride (HCl) gas)flow is introduced to the growth zone (e.g.,200-1100 sccm, 400-900 sccm) at block 214. After the metal halideprecursors flow is turned off, the halogen gas or the hydrogen halidegas can keep flowing for a time period (e.g., 0-5 minutes) at block 216The buffer layer is deposited based on the reaction of the ammonia, oneor more metal halide precursors, and a halogen gas or a hydrogen halidegas in the growth zone. For example, AlN buffer layer is deposited basedon the reaction of the ammonia, aluminum halide precursor, and chlorinegas (or hydrogen chloride gas) in the growth zone. For example, AlGaNbuffer layer is deposited based on the reaction of the ammonia, aluminumhalide precursor, gallium halide precursor and chlorine gas (or hydrogenchloride gas) in the growth zone. The halogen gas (e.g., chlorine (Cl2)gas) or a hydrogen halide gas (e.g., hydrogen chloride (HCl) gas) in thegrowth zone suppresses homogeneous particle formation during the bufferdeposition operation.

After the halogen gas or hydrogen halide gas is turned off and thebuffer layer formation is completed, the temperature of the substratecarrier ramps to a third temperature (e.g., temperature greater than 900degrees C., 980-1080 degrees C.) at block 217. Once carrier temperaturereaches the third temperature the Ammonia flow switches to a flow rate(e.g., 2-20 SLM, 2-4 SLM) at block 218.

The substrate with buffer layer goes under the second nitridization fora certain time period (e.g., 10 minutes) at block 220. After thenitridization, the carrier temperature ramps to a fourth temperature(e.g., temperature of 900 degrees C. or higher, 980-1080 degrees C.) atblock 222. During this operation, ammonia flow switches to 1-22 SLM.Once the substrate carrier temperature reaches the fourth temperature,chlorine (Cl2) gas flow over a metal source (e.g., Ga source) isintroduced to a flow rate (e.g., 50-400 sccm) for group III-nitridegrowth (e.g., GaN growth) at block 224. After a 3-30 minute deposition,when the desired GaN thickness is achieved, the chlorine gas flow overthe metal source is interrupted and the substrate carrier is cooled downwhile flowing ammonia gas to preserve the group III-nitride layer. In analternative embodiment, the chlorine (Cl2) flow of operation 224 isreplaced with hydrogen chloride (HCl) flow.

In one embodiment, 5 μm thick GaN layers have been grown using processconditions described above with a growth rate between 12 and 60 μm/hr.The roughness of the GaN layers is in the range of 2-3 nm. The layerquality has been investigated by X-ray diffraction. The FWHM ofreflections (002) and (102) is used to determine the tilt and twiststructure of the GaN layer. The FWHM of the {acute over (ω)}-scanrocking curves for (002) and (102) reflections for 5 μm thick GaN layersare in the range of 200-300 arcsec and 280-380 arcsec, respectively.

FIG. 3 a illustrates an AFM image 300 of a 1 micron by 1 micron sapphiresubstrate surface. FIGS. 3 b-f illustrate the effect of additional Cl2flow on a surface morphology of a high temperature AlN buffer layerdeposited on the sapphire substrate in accordance with one embodiment.These high temperature AlN buffer layers are deposited based on thereaction of the ammonia (NH3) gas, aluminum trichloride (AlCl3) gas, andadditional chlorine gas (Cl2) gas in the growth zone. The additionalchlorine gas in the growth zone suppresses homogeneous particleformation during the buffer deposition operation. Aluminum trichloridewas created by a reaction of Cl2 with solid Al pellets at about 550degrees C. in the Al source zone of the reactor and delivered to thedeposition chamber with N2 carrier gas. FIG. 3 b illustrates the AFMimage 310 of an AlN buffer layer that was deposited with no additionalCl2 flow in the growth zone. FIG. 3 c illustrates the AFM image 320 ofan AlN buffer layer that was deposited with an additional Cl2 flow of100 sccm in the growth zone. FIG. 3 d illustrates the AFM image 330 ofan AlN buffer layer that was deposited with an additional Cl2 flow of300 sccm in the growth zone. FIG. 3 e illustrates the AFM image 340 ofan AlN buffer layer that was deposited with an additional Cl2 flow of500 sccm in the growth zone. FIG. 3 f illustrates the AFM image 350 ofan AlN buffer layer that was deposited with an additional Cl2 flow of800 sccm in the growth zone. The AlN buffer layer becomes thicker with ahigher flow of Cl2. The surface becomes rougher with an increasingthickness of AlN buffer.

FIG. 4 illustrates the root-mean-square roughness (Rms) in nanometers ofhigh temperature AlN buffers that are deposited on a sapphire substrateat different flows of additional Cl2 during the AlN deposition operationin accordance with one embodiment. The deposition of AlN withoutadditional Cl2 is negligible. The Rms value for a sapphire substrate,which is illustrated in FIG. 3 a, is 0.146 nm while the Rms value forAlN without additional Cl2, which is illustrated in FIG. 3 b is 0.204nm. The AlN buffer layer becomes thicker with a higher flow of Cl2. Thesurface becomes rougher with an increasing thickness of AlN buffer.

The buffer techniques with suppression of homogeneous particlesformation described in the present disclosure can be used together toform multi buffer techniques. For example, some combinations of lowtemperature buffers (e.g., AlN, AlGaN) and high temperature (e.g., AlN,AlGaN) buffers may be used to improve crystal quality and morphology ofgroup III-nitride materials. The multi buffer techniques can also reduceor tune the stress in the subsequently deposited layers and final devicestructures. The buffer may be deposited on the substrate, or on thesurface of another buffer. The additional buffer layers may be added asinterlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).

FIGS. 5 a-f illustrate several examples of locations of multiple buffersfor GaN deposition on a sapphire structure with a HVPE system inaccordance with one embodiment. The device 500 illustrated in FIG. 5 aincludes a sapphire substrate 502, a high temperature AlN buffer layer504, a GaN layer 506, a low temperature AlN buffer layer 508, and a GaNlayer 509. The device 510 illustrated in FIG. 5 b includes a sapphiresubstrate 512, a low temperature AlN buffer layer 514, a GaN layer 516,a low temperature AlN buffer layer 518, and a GaN layer 519. The device520 illustrated in FIG. 5 c includes a sapphire substrate 522, a lowtemperature AlN buffer layer 524, a high temperature AlGaN buffer layer526, and a GaN layer 528. The device 530 illustrated in FIG. 5 dincludes a sapphire substrate 532, a low temperature AlN buffer layer534, a high temperature AlN buffer layer 536, and a GaN layer 538. Thedevice 540 illustrated in FIG. 5 e includes a sapphire substrate 542, ahigh temperature AlN buffer layer 544, a high temperature AlGaN bufferlayer 546, and a GaN layer 548. The device 510 illustrated in FIG. 5 fincludes a sapphire substrate 552, a low temperature AlN buffer layer554, a high temperature AlN buffer layer 556, a high temperature AlGaNbuffer layer 558, and a GaN layer 559.

In one embodiment, the devices 500, 510, 520, 530, 540, and 550 includeadditional layers deposited with the HVPE system or a MOCVD system. Forexample, the additional layers (to create III-nitride device structure)may include InGaN MQW, p-type AlGaN, and p-type GaN. The additionallayers may include n-type AlGaN, InGaN, InGaN/GaN MQW, GaN, p-typeAlGaN, and p-type GaN. In other embodiments, the sapphire substrate maybe replaced with a silicon substrate, a SiC substrate, lithium aluminumoxide, lithium gallium oxide, zinc oxide, GaN, AlN, quartz, glass, GaAs,spinel, any combination thereof, any mixture thereof, or any alloythereof.

For a single chamber process, layers of differing composition are grownsuccessively as different operations of a growth recipe executed withinthe single chamber. For a multiple chamber process, layers inIII-nitride device structure (e.g., LED, LD) are grown in a sequence ofseparate chambers. For example, an undoped/nGaN layer or the layersillustrated in FIG. 5 a-5 f may be grown in a first chamber, a MQWstructure grown in a second chamber, and a p-type GaN layer or p-typeAlGaN grown in a third chamber.

FIG. 6 illustrates a method for enhancing growth of a high-quality groupIII-nitride (e.g., GaN, AlN, AlGaN) thin layer with multiple bufferlayers grown in a HVPE system on a suitable substrate (e.g., aluminumoxide containing substrate, sapphire substrate, (0001) sapphiresubstrate) in accordance with one embodiment (e.g., as illustrated inFIGS. 5 c and 5 d). The method includes growing an in situ lowtemperature group III-nitride initial layer that contains aluminum(e.g., AlN initial layer, AlGaN initial layer) on a substrate. Then, anin situ high temperature group III-nitride buffer layer that containsaluminum (e.g., AlN buffer, AlGaN buffer) is grown on the initial layer.Subsequently, a high temperature high-quality GaN deposition occurs inthe HVPE system. The multiple buffer layers are grown while suppressinghomogeneous particle formation.

At block 602, a substrate (e.g., sapphire substrate) is provided for thegrowth of a group III-nitride (e.g., GaN, AlN, AlGaN). At block 604, thesubstrate is loaded on a substrate carrier into a HVPE system. Then, theinitial process conditions for the system are established at block 606.The process conditions may include setting the pressure (e.g., 50-800Torr, 400-450 Torr), setting the nitrogen containing material (e.g,nitrogen gas, nitrous oxide, ammonia, hydrazine, diimide, hydrazoicacid, etc) to a flow rate (e.g., 2-10 SLM, 2-4 SLM), and ramping thesubstrate carrier temperature to a first temperature (e.g., temperaturegreater than 900 degrees C., 950-1050 degrees C.). Once the temperaturereaches the set point, the substrate is under nitridization for a timeperiod (e.g., 5-15 minutes) at block 608. After nitridization, thesubstrate carrier is cooled down to a second temperature (e.g.,temperature less than 900 degrees C., 500-800 degrees C., 600-700degrees C.) at block 610 for low temperature deposition.

When the temperature set point is reached, a low temperature groupIII-nitride buffer layer containing aluminum (e.g., AlN, AlGaN)deposition starts at block 612. The initial layer is grown whilesuppressing homogenous particle formation (e.g., AlN, AlGaN) based onflowing a halogen gas (e.g., additional chlorine) or a hydrogen halide(e.g., additional HCl gas) to the growth zone. The process conditionsfor the buffer layer deposition may include flowing one or more metalhalide precursors (e.g., at least one aluminum halide containingprecursor (e.g., AlCl3, AlCl, AlBr, AlBr3, AlI, AlI3, GaCl, GaCl3,etc.)) with a carrier gas into the growth zone of the HVPE system atblock 612. An aluminum chloride precursor may be formed by flowingchlorine gas (Cl2) to a metal source (e.g., an aluminum source) locatedin separate zone (upstream of the deposition zone) at a flow rate andtime period (e.g., 10-150 sccm for 30 seconds to 5 minutes).Alternatively, HCl gas is flowed over an Al source to form the aluminumchloride precursor at a flow rate and time period (e.g., 20-300 sccm for30 seconds to 5 minutes). The Al source may be solid and have atemperature from 200 degrees C. to the Al melting point temperature(e.g., about 660 degrees C.). The Al source may be liquid and have atemperature greater than the Al melting point temperature. In anotherembodiment, a source of liquid Ga is also used to form a galliumchloride precursor (e.g., GaCl, GaCl3) in separate zone upstream of thedeposition zone.

At the same or approximately the same time (e.g., 0-1 min before) of theintroduction of the metal halide precursors into the growth zone, ahalogen gas (e.g., chlorine (Cl2) gas) or a hydrogen halide gas (e.g.,hydrogen chloride (HCl) gas)flow is introduced to the growth zone (e.g.,200-1100 sccm, 400-900 sccm) at block 616. After the metal halideprecursors flow is turned off, the halogen gas or hydrogen halide gasflow can keep flowing for a time period (e.g., 0-5 minutes) at block618. The initial or buffer layer is deposited based on the reaction ofthe ammonia, one or more metal halide precursors, and a halogen gas or ahydrogen halide gas in the growth zone.

After the halogen gas or hydrogen halide gas flow is turned off, thetemperature of the substrate carrier starts to ramp to a thirdtemperature (e.g., temperature greater than 900 degrees C., 980-1080degrees C.) at block 620. During this operation, ammonia flow switchesto 1-12 SLM. Once the substrate carrier reaches the third temperature,then high temperature group III-nitride buffer layer containing aluminum(e.g., AlN, AlGaN) deposition starts at block 624. The high temperaturebuffer layer is grown while suppressing homogenous particle formation(e.g., AlN, AlGaN) based on flowing a halogen gas or hydrogen halide gasto the growth zone. The process conditions for the high temperaturebuffer layer deposition may include flowing one or more metal halideprecursors (e.g., at least one aluminum halide containing precursor(e.g., AlCl3, AlCl, AlBr, AlBr3, AlI, AlI3, GaCl, GaCl3, etc.)) with acarrier gas into the growth zone of the HVPE system at block at block624. An aluminum chloride precursor may be formed by flowing chlorinegas (Cl2) to a metal source (e.g., an aluminum source) located inseparate zone (upstream of the deposition zone) at a flow rate and timeperiod (e.g., 10-150 sccm for 30 seconds to 5 minutes). Alternatively,HCl gas is flowed over an Al source to form the aluminum chlorideprecursor at a flow rate and time period (e.g., 20-300 sccm for 30seconds to 5 minutes). The Al source may be solid and have a temperaturefrom 200 degrees C. to the Al melting point temperature (e.g., about 660degrees C.). The Al source may be liquid and have a temperature greaterthan the Al melting point temperature. In another embodiment, a sourceof liquid Ga is also used to form a gallium chloride precursor (e.g.,GaCl, GaCl3) in separate zone upstream of the deposition zone.

At the same or approximately the same time (e.g., 0-1 min before) of theintroduction of the metal halide precursors into the growth zone, ahalogen gas (e.g., chlorine (Cl2) gas) or a hydrogen halide gas (e.g.,hydrogen chloride (HCl) gas)flow is introduced to the growth zone (e.g.,200-1100 sccm, 400-900 sccm) at block 626. After the metal halideprecursors flow is turned off, the halogen gas or hydrogen halide gasflow can keep flowing for a time period (e.g., 0-5 minutes) at block628. The high temperature buffer layer is deposited based on thereaction of the ammonia, one or more metal halide precursors, and ahalogen gas or hydrogen halide gas in the growth zone.

After the halogen gas or hydrogen halide gas flow is turned off and thebuffer layer formation is completed, the temperature of the substratecarrier ramps to a fourth temperature (e.g., temperature greater than900 degrees C., 980-1080 degrees C.) at block 630. Once carriertemperature reaches the fourth temperature, then the Ammonia flowswitches to a flow rate (e.g., 2-20 SLM, 2-4 SLM) at block 632.

The substrate with buffer layer goes under the second nitridization fora certain time period (e.g., 10 minutes) at block 634. After thenitridization, the carrier temperature ramps to a fifth temperature(e.g., temperature of 900 degrees C. or higher, 980-1080 degrees C.) atblock 636. During this operation, ammonia flow switches to 1-22 SLM.Once the substrate carrier temperature reaches the fifth temperature,chlorine (Cl2) gas flow over a metal source (e.g., Ga source) isintroduced to a flow rate (e.g., 50-400 sccm) for group III-nitridegrowth (e.g., GaN growth) at block 638. After a 3-30 minute deposition,when the desired GaN thickness is achieved, the chlorine gas flow overthe metal source is interrupted and the substrate carrier is cooled downwhile flowing ammonia gas to preserve the group III-nitride layer. In analternative embodiment, the chlorine (Cl2) flow of operation 638 isreplaced with hydrogen chloride (HCl) flow.

The crystalline quality of the GaN layers grown on sapphire substratesaccording the present disclosure with group III-nitride buffer layerscontaining aluminum deposited with suppression of homogeneous particleformation is at least comparable to and likely superior to thehighest-quality GaN films grown by MOCVD and HVPE reported in theliterature. Typical full widths at half-maximum (FWHM) of X-ray rockingcurve measurements for the 5-6 μm thick GaN films grown on a (0001)sapphire according to the present disclosure with combination of lowtemperature AlN and high temperature AlN buffers (according with FIG. 5d scheme) are 90-130 arcsec for the on-axis (002) peak and 230-280arcsec for the off-axis (102) peak.

FIG. 7 a illustrates an X-ray rocking curve for on-axis (002) peak andFIG. 7 b illustrates an X-ray rocking curve for an off-axis (102) peakfor 4.8 μm GaN deposited on a (0001) sapphire substrate in a HVPE systemin accordance with one embodiment. The GaN is deposited according to thepresent disclosure with combination of low temperature AlN and hightemperature AlN buffers (according with FIG. 5 d scheme), which aregrown with suppression of homogeneous particles formation by flowing theadditional chlorine (Cl2) gas. The low temperature AlN buffer isdeposited on (0001) sapphire substrate in a HVPE system.

The reactor conditions will vary by reactor type and design. The threemethods described above for FIGS. 1, 2, and 6 show only three sets ofconditions that have been found to be useful for the group III-nitridebuffer (that contains aluminum) growth with suppression of homogeneousformation and subsequent high quality group III-nitride epitaxial layerdeposition. Other conditions may also be useful for such growth.

Note that operations in FIGS. 1, 2, and 6 may be omitted or additionaloperations may be added as desired. The chamber pressures may bedifferent for nitridation, AlN buffer deposition, AlGaN bufferdeposition, and GaN deposition operations. There are other operationsthat could vary in the growth process. It has been found thatnitridization of the substrates and nitridization of the groupIII-nitride buffer layers that contains aluminum improve surfacemorphology for some high quality group III-nitride epitaxial layers, andimprove crystal quality for other layers. However, this may or may notbe necessary for any particular growth technique.

Any carrier gas may be used in this application. Typically carrier gasesare nitrogen (N2), hydrogen (H2), argon (Ar) or helium (He), or anycombination of these gases.

In one embodiment, the Al-containing group III-nitride buffers of thepresent disclosure can be used for subsequent growth of any nitridealloy composition and any number of layers or combination thereof, forexample, the group III-nitride thin layers may include an alloycomposition of (Ga, Al, In, B)N semiconductors having a formulaGanAlxInyBzN where 0≦n≦1, 0≦x≦1, 0≦y≦1, 0≦z≦1 and n+x+y+z=1.

Dopants, such as Zn, Fe, Si, Ge, and Mg, are frequently doped intonitride layers. The incorporation of these and other dopants notspecifically listed is compatible with the practice of this disclosure.

Structural substrates that may be used for embodiments of the inventioninclude, but are not limited to, silicon (Si), silicon carbide (SiC),sapphire or other forms of aluminum oxide (Al2O3), lithium aluminumoxide (LiAlO2), lithium gallium oxide (LiGaO2), zinc oxide (ZnO),gallium nitride (GaN), aluminum nitride (AlN), quartz, glass, galliumarsenide (GaAs), spinel (MgAl2O4), any combination thereof, any mixturethereof, or any alloy thereof. The present disclosure may be used fordeposition of AlN (or group III-nitride semiconductor containingaluminum) in any orientation, e.g., semi-polar, non-polar, and polar.So, different orientations of the substrates may be used. Theintentional miscut from crystallographic planes of the substrates may bealso used to improve the crystal quality and morphology of nitridelayers on the substrates. The intentional miscut can be used to initiatethe 2D growth mode deposition of nitride layers.

The present disclosure can also be used for depositing group III-nitridelayers using any patterned substrates with different patterns geometry.In one embodiment, the patterned substrate is a (0001) patternedsapphire substrate (PSS). Patterned sapphire substrates may be extremelyuseful in the manufacturing of LEDs and LDs because they increase thelight extraction efficiency. Another benefit of using PSS is possibleGaN crystal quality improvement.

All CVD epitaxial methods where any aluminum halide and ammonia exist inform of any adduct (ammonia complex of aluminum halides) or separatelydelivered and mixed just during a deposition operation to create groupIII-nitride semiconductor layer(s) containing aluminum may be attributedto containing Al HVPE process. The present disclosure is related to Alcontaining HVPE process.

The aluminum halides contained precursors may be located in the specialreactor zone of the HVPE reactor or contained inside the bubbler (e.g.,evaporator) which is connected by a delivery line to the HVPE reactor.The aluminum halides contained precursors are maintained at a constanttemperature to provide sufficient vapor pressure of the aluminum halide,which is carried into the premixing zone or in the deposition zone bycarrier gas.

The aluminum halides may be generated by a chemical reaction of Allocated in the special reactor zone with halogen gas or hydrogen halidegas. Any halogen or combination of halogens selected from the groupconsisting of Cl2, Br2, I2 may be used for reaction with Al to createaluminum monohalides or aluminum trihalides. Any hydrogen halide orcombination of hydrogen halides selected from the group consisting ofHCl, HBr, HI may be used for reaction with Al to create aluminummonohalides or aluminum trihalides.

A general outline of growth parameters for AlN (or group III-nitridesemiconductor crystals containing aluminum) deposition is a pressurebetween 10 Torr and 1000 Torr, and a temperature between 400 degrees C.and 1400 degrees C. The reactor conditions for group III-nitridesemiconductor compounds containing aluminum (e.g., AlN) deposition mayvary according to individual reactors design and type of aluminum halidesources (e.g., AlCl3, AlCl3-NH3, AlBr3 or (AlCl3)-nNH3, AlCl).

FIG. 8 is a schematic sectional view of an HVPE apparatus 800 which canbe used to deposit group III-nitride layers (e.g., GaN, AlN, AlGaN,AlON) formed using the processes described herein. The HVPE apparatus800 includes a chamber 802 enclosed by a lid 804. The chamber 802 andthe lid 804 define a processing zone (or growth zone) 807. A showerhead806 is disposed in an upper region of the processing zone 807. Asusceptor 814 is disposed opposing the showerhead 606 in the processingzone 807. The susceptor 814 is configured to support a plurality ofsubstrates 815 thereon during processing. In one embodiment, thesubstrates 815 are disposed on a substrate carrier 816 which issupported by the susceptor 814. The susceptor 614 may be rotated by amotor 860, and may be formed from a variety of materials, including SiCor SiC-coated graphite.

In one embodiment, the HVPE apparatus 800 includes a heating assembly828 configured to heat the substrates 815 on the susceptor 814. in oneembodiment, chamber bottom 802A is formed from quartz and the heatingassembly 828 is a lamp assembly disposed under the chamber bottom 802Ato heat the substrates 815 through the quartz chamber bottom 802A, inone embodiment, the heating assembly 828 includes an array of lamps thatare distributed to provide a uniform temperature distribution across thesubstrates, substrate carrier, and/or susceptor.

The HVPE apparatus 800 further includes precursor supplying pipes 822,824 disposed inside the side wall 808 of the chamber 802. The pipes 822and 824 are in fluid communication with the processing zone 807 and annet tube 821 found in a precursor source module 832. The showerhead 806is in fluid communication with the processing zone 807 and a first gassource 810. The processing zone 807 is in fluid communication with anexhaust 851 through an cutlet 826.

The HVPE apparatus 800 further includes a heater 830 embedded within thewas 808 of the chamber 802. The heater 830 embedded in the walls 808 mayprovide additional heat if needed during the deposition process. Athermocouple may be used to measure the temperature inside theprocessing chamber. Output from the thermocouple may be fed back to acontroller 841 that controls the temperature of the walls of the chamber802 by adjusting the power delivered to the heater 830 (e.g., resistiveheating elements) based upon the reading from a thermocouple (notshown). For example, if the chamber is too cool, the heater 630 will beturned on. If the chamber is too hot, the heater 830 will be turned off.Additionally, the amount of heat provided from the heater 830 may becontrolled so that the amount of heat provided from the heater 830 isminimized.

Processing gas from the first gas source 810 is delivered to theprocessing zone 807 through the gas distribution showerhead 806. in oneembodiment, the first gas source 810 is an ammonia gas source. in oneembodiment, the first gas source 810 is configured to deliver a gas thatincludes ammonia or nitrogen, in one embodiment, an inert gas (e.g., He,Ar, N2) may be introduced as well either through the gas distributionshowerhead 606 or through the pipe 624, disposed on the was 808 of thechamber 802. In one embodiment, chlorine gas may be introduced throughthe pipe 824, disposed on the walls 608 of the chamber 802. An energysource 812 may be disposed between the first gas source 810 and the gasdistribution showerhead 806. In one embodiment, the energy source 812may include a heater or a remote RF plasma source.

The source module 832 includes a halogen or hydrogen halide gas source818 connected to a well 834A of a source boat and an inert gas source634 connected to the well 634A. A source material 823, such as aluminum,gallium or indium, is disposed in the well 834A. A heating source 820surrounds the source boat. An inlet tub 621 connects the well 834A tothe processing zone 807 via the pipes 822, 824.

In one embodiment, during processing a halogen gas (e.g., Cl2, Br2 orI2) is delivered from the halogen gas source 818 to the well 834A of thesource boat to create a metal halide precursor gas. In one embodiment,during processing a hydrogen halide gas (e.g., HCl, HBr or HI) isdelivered from the hydrogen halide gas source 818 to the well 834A ofthe source boat to create a metal halide precursor gas. The interactionof the halogen gas or hydrogen halide gas and the solid or liquid sourcematerial 823 allows a metal halide precursor to be formed. In oneembodiment, the metal halide gas is a group III metal halide gas, suchas gallium chloride (e.g., GaCl, GaCl3), indium chloride (e.g., InCl3)or aluminum chloride (e.g., AlCl3, AlCl). The source boat may be heatedby the heating source 820 to heat the source material 823 and allow themetal halide precursor to be formed. The metal halide precursor is thendelivered to the processing zone 807 of the HVPE apparatus 800 throughan inlet tube 821. In one embodiment, an inert gas (e.g., Ar, He, N2)delivered from the inert gas source 834 is used to carry, or push, themetal halide precursor formed in the well 834A through the inlet tube821 and pipes 822 and 824 to the processing zone 807 of the HVPEapparatus 800. An ammonia gas (NH3) may be introduced into theprocessing zone 607 through the showerhead 606, while the metal halideprecursor is also provided to the processing zone 807, so that a groupIII-nitride layer can be formed on the surface of the substrates 815disposed in the processing zone 807.

In another embodiment, one or more substrates may be provided in a onechamber first to form a group III-nitride layer that contains aluminum,and then move to a different chamber within a tool for subsequentprocessing. FIG. 9 is a cluster tool 900 may be used in a processaccording to one embodiment of the present disclosure. The cluster tool900 is configured to form nitride compound structures.

In one embodiment, the cluster tool 1600 includes one HVPE chamber 1602and multiple MOCVD chambers 1603 a and 1603 b connected to a transferchamber 1606 for fabricating compound nitride semiconductor devicesaccording to embodiments described herein. Although one HVPE chamber1602 and two MOCVD chambers 1603 a and 1603 b are shown, it should beunderstood that any combination of one or more MOCVD chambers with oneor more HVPE chambers may also be coupled with the transfer chamber1606. For example, in one embodiment, the cluster tool 1600 may include3 MOCVD chambers It should also be understood that although a clustertool is shown, the embodiments described herein may also be performedusing a linear processing system.

In one embodiment, an additional chamber 1604 is coupled with thetransfer chamber 1606. The additional chamber 1604 may be an MOCVDchamber, an HVPE chamber, a metrology chamber, a degassing chamber, anorientation chamber, a cool down chamber, a pretreatment/precleanchamber, a post-anneal chamber, or the like. In one embodiment, thetransfer chamber 1606 is six-sided and hexagonal in shape with sixpositions for process chamber mounting. In another embodiment, thetransfer chamber 1606 may have other shapes and have five, seven, eight,or more sides with a corresponding number of process chamber mountingpositions.

The HVPE chamber 1602 is adapted to perform HVPE processes in whichgaseous metal halides are used to epitaxially grow layers of compoundnitride semiconductor materials on heated substrates. The HVPE chamber1602 includes a chamber body 1614 where a substrate is placed to undergoprocessing, a chemical delivery module 1618 from which gas precursorsare delivered to the chamber body 1614, and an electrical module 1622that includes the electrical system for the HVPE chamber of the clustertool 1600. In one embodiment, the HVPE chamber 1602 may be similar tothe HVPE apparatus 600 described in FIG. 7.

Each MOCVD chamber 1603 a, 1603 b includes a chamber body 1612 a, 1612 bforming a processing region where a substrate is placed to undergoprocessing, a chemical delivery module 1616 a, 1616 b from which gasessuch as precursors, purge gases, and cleaning gases are delivered to thechamber body 1612 a, 1612 b and an electrical module 1620 a, 1620 b foreach MOCVD chamber 1603 a, 1603 b that includes the electrical systemfor each MOCVD chamber of the cluster tool 1600. Each MOCVD chamber 1603a, 1603 b is adapted to perform CVD processes in which metalorganicprecursors (e.g., TMG, TMA) react with metal hydride elements to formlayers of compound nitride semiconductor materials.

The cluster tool 1600 further includes a robot assembly 1607 housed inthe transfer chamber 1606, a load lock chamber 1608 coupled with thetransfer chamber 1606, a batch load lock chamber 1609, for storingsubstrates, coupled with the transfer chamber 1606. The cluster tool1600 further includes a load station 1610, for loading substrates,coupled with the load lock chamber 1608. The robot assembly 1607 isoperable to pick up and transfer substrates between the load lockchamber 1608, the batch load lock chamber 1609, the HVPE chamber 1602,and the MOCVD chambers 1603 a, 1603 b. In one embodiment, the loadstation 1610 is an automatic loading station configured to loadsubstrates from cassettes to substrate carriers or to the load lockchamber 1608 directly, and to unload the substrates from substratecarriers or from the load lock chamber 1608 to cassettes.

The transfer chamber 1606 may remain under vacuum and/or at a pressurebelow atmosphere during the process. The vacuum level of the transferchamber 1606 may be adjusted to match the vacuum level of correspondingprocessing chambers. In one embodiment, the transfer chamber 1606maintains an environment having greater than 90% N2 for substratetransfer. In another embodiment, the transfer chamber 1606 maintains anenvironment of high purity NH3 for substrate transfer. In oneembodiment, the substrate is transferred in an environment havinggreater than 90% NH3. In another embodiment, the transfer chamber 1606maintains an environment of high purity H2 for substrate transfer. Inone embodiment, the substrate is transferred in an environment havinggreater than 90% H2.

The cluster tool 1600 further includes a system controller 1660 whichcontrols activities and operating parameters. The system controller 1660includes a computer processor and a computer-readable memory coupled tothe processor. The processor executes system control software, such as acomputer program stored in memory.

In one embodiment, one of the processing chamber 1602, 1603 a, 1603 b,or 1604 is configured to form a group III-nitride layer that containsaluminum according to methods described above prior to forming devicestructures. The group III-nitride layer that contains aluminum orseveral group III-nitride layers deposited on substrates according tomethods described above are then transferred to one or more depositionchambers to deposit the subsequent layers used to form the LED or LDstructures. In one embodiment, the group III-nitride buffer layer thatcontains aluminum may be deposited on substrates and/or covered with aIII-nitride layers (e.g., undoped GaN layer, n-doped GaN layer) in theHVPE processing chamber 1602, then moved to MOCVD processing chambers1603 a or/and 1603 b for forming group III-nitride layers for the devicestructure (e.g., n-doped GaN layer, AlGaN layer, MQW structure, p-dopedAlGaN layer, p-doped GaN layer). In another embodiment, the groupIII-nitride buffer layer that contains aluminum may be deposited onsubstrates in the HVPE processing chamber 1602, then moved to MOCVDprocessing chambers 1603 a or/and 1603 b for forming subsequent layersfor the device structure.

FIG. 10 illustrates a cross-sectional view of a power electronics devicein accordance with one embodiment. The power electronic device 1200 mayinclude an N type region 1210 (e.g., electrode), ion implanted regions1212 and 1214, an epitaxial layer 1216 (e.g., N type GaN epi layer witha thickness of 4 microns), a buffer layer (e.g., N+ GaN buffer layerwith a thickness of 2 microns), a substrate 1220 (e.g., N+ bulk GaNsubstrate, silicon substrate), and an ohmic contact (e.g., Ti/Al/Ni/Au).The device 1200 may include one or more layers of GaN disposed on a GaNsubstrate or a silicon substrate. The device (e.g., power IC, powerdiode, power thyristor, power MOSFET, IGBT, GaN HEMT transistor) may beused for switches or rectifiers in power electronics circuits andmodules.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. Although the present disclosure has been describedwith reference to specific exemplary embodiments, it will be recognizedthat the invention is not limited to the embodiments described, but canbe practiced with modification and alteration. Accordingly, thespecification and drawings are to be regarded in an illustrative senserather than a restrictive sense.

What is claimed is:
 1. A method of depositing multiple buffer layers ina processing chamber of a hydride vapor phase epitaxy processing system,comprising: providing a substrate in the processing chamber of thehydride vapor phase epitaxy processing system; forming a first group IIInitride buffer layer that contains aluminum by flowing ammonia gas to agrowth zone of the processing chamber, flowing one or more metal halidecontaining precursors including at least one aluminum halide containingprecursor, and flowing halogen gas or hydrogen halide gas into thegrowth zone at the same time; and forming a second group III nitridebuffer layer that contains aluminum over the first buffer layer byflowing ammonia gas to a growth zone of the processing chamber, flowingone or more metal halide containing precursors including at least onealuminum halide containing precursor, and flowing halogen gas orhydrogen halide gas into the growth zone at the same time, wherein thefirst group III-nitride buffer layer is aluminum nitride (AlN) layerformed at a temperature of approximately 500 to 800 degrees Celsius, thesecond group III-nitride buffer layer is aluminum nitride (AlN) layerformed at a temperature of 900 degrees Celsius or higher.
 2. The methodof claim 1, further comprising: forming a group III-nitride layer overthe buffer layers, wherein the first group III nitride buffer layercomprises an initial layer or a nucleation layer.
 3. The method of claim2, wherein the group III-nitride layer is formed by reacting the atleast one metal halide containing precursor and ammonia gas.
 4. Themethod of claim 1, wherein the aluminum halide containing precursorcomprises an aluminum chloride gas, wherein the hydrogen halide gascomprises a hydrogen chloride (HCl) gas.
 5. The method of claim 1,wherein the halogen gas comprises a chlorine (Cl2) gas.
 6. The method ofclaim 1, wherein the halogen gas or hydrogen halide gas that is flowedinto the growth zone suppresses homogeneous formation of particles. 7.The method of claim 1, further comprising: stopping the flow of allmetal halide containing precursors while continuing to flow the halogengas or hydrogen halide gas and ammonia into the growth zone of theprocessing chamber for a time period.
 8. The method of claim 1, whereinthe one or more metal halide containing precursors comprise at least oneof an aluminum trichloride (AlCl3) precursor, an aluminum monochloride(AlCl) precursor, an aluminum tribromide (AlBr3) precursor, a galliummonochloride (GaCl) precursor, and a gallium trichloride (GaCl3)precursor.
 9. The method of claim 1, further comprising: forming a thirdgroup III-nitride buffer layer that contains aluminum over the secondbuffer layer by flowing ammonia gas to a growth zone of the processingchamber, flowing one or more metal halide containing precursorsincluding at least one aluminum halide containing precursor, and flowinghalogen gas or hydrogen halide gas into the growth zone at the sametime; and forming a group III-nitride layer over the third buffer layer.10. A method, comprising: providing a substrate in a processing chamber;forming a first group III-nitride buffer layer that contains aluminum byflowing ammonia gas to a growth zone of the processing chamber, flowingone or more metal halide containing precursors, and flowing halogen gasor hydrogen halide gas into the growth zone at the same time; forming afirst group III-nitride layer over the first buffer layer; forming asecond group III-nitride buffer layer that contains aluminum over thefirst group III-nitride layer by flowing ammonia gas to a growth zone ofthe processing chamber, flowing one or more metal halide containingprecursors, and flowing halogen gas or hydrogen halide gas into thegrowth zone at the same time; and forming a second group III-nitridelayer over the second group III-nitride buffer layer that containsaluminum, wherein the first group III-nitride buffer layer is aluminumnitride (AlN) layer formed at a temperature of approximately 500 to 800degrees Celsius, the second group III-nitride buffer layer is aluminumnitride (AlN) layer formed at a temperature of 900 degrees Celsius orhigher.
 11. The method of claim 10, wherein the first and second groupIII-nitride layers are formed by reacting the at least one metal halidecontaining precursor and ammonia gas.
 12. The method of claim 10,wherein the one or more metal halide containing precursors include atleast one aluminum halide containing precursor, wherein the hydrogenhalide gas is a hydrogen chloride (HCl) gas.
 13. The method of claim 10,wherein the halogen gas is a chlorine (Cl2) gas.
 14. The method of claim10, wherein the halogen gas or hydrogen halide gas that is flowed intothe growth zone suppresses homogeneous formation of particles.
 15. Themethod of claim 10, wherein the substrate is sapphire substrate.
 16. Themethod of claim 10, further comprising: stopping the flow of all metalhalide containing precursors while continuing to flow the halogen gas orhydrogen halide gas and ammonia into the growth zone of the processingchamber for a time period.
 17. The method of claim 10, wherein the oneor more metal halide containing precursors comprise at least one of analuminum trichloride (AlCl3) precursor, an aluminum monochloride (AlCl)precursor, an aluminum tribromide (AlBr3) precursor, a galliummonochloride (GaCl) precursor, and a gallium trichloride (GaCl3)precursor.